Research On On-line Monitoring And Fault Diagnosis Techniques For On-load Tap Changers' Characteristics

On-load tap changers(OLTC) which play an important role in stabilizing the load voltage and regulating reactive power flows, are the essential components of on-load tap changing transformers.However, statistics have shown that more than 20% of power transformer accidents are caused by OLTC failures and most OLTC failures are mechanical failures. As a result, it is of great importance for the security and stable operation of electrical power system to on-line monitor the operating performance of OLTC.Considering the close relationship between practical OLTC vibration signals and its operating performance, a dynamics analysze method utilizing the phase space reconstruction is proposed to analyze the chaotic characteristic of practical OLTC vibration signals. By calculating the embeddig dimension and time delay, vibration signals are reconstructed to extract feature of vibration signals efficiently. Furthermore, the chaos characteristic of vibration signals is confirmed in theory utilizing the maximum Lyapunov exponent.As the orbit of OLTC vibration signals in reconstructed phase space is closely related to running state of OLTC, the distributions of orbits is analyzed with lucubrate direction. Based on theory of cluster analysis, the phase point distribution density is proposed to extract feature of orbit distribution.Comparing with an existed coefficient, the phase point distribution coefficient(PPDC), the phase point distribution density can extract feature of signals more quickly with higher resolution.To improve the accuracy of on-line monitoring and fault diagnosis of OLTC, the fuzzy set theory is utilized to describe the characteristics of fuzziness and probability of OLTC fault. The fuzzy fault diagnosis method can build the mapping process from the feature of signals to diagnosis result. The types of OLTC fault are defined as the distribution of fuzzy sets and the subordination is employed to handle OLTC mechanical condition determination fuzzy question. The proposed system can identify faults efficiently.To meet the need of practical OLTC on-line monitoring, an effective OLTC on-line test system is designed and manufactured to obtain vibration signals based on the LabVIEW/CompactRIO.platform.The testing results of OLTC vibration signals show, this system can obtain the vibration signals efficiently and assess the state of OLTC accurately with the embedded analysis software. Furthermore,the on-line test system is designed to adapt the complicated electromagnetic environment in the substation.